Thermostatic control device using a hall plate



W. V. DE FOREST Oct. 15, 1968 THERMOSTATIC CONTROL DEVICE USING A HALL PLATE 3 Sheets-Sheet 1 Filed June 23 1967 TUE INVENTOR WESLEY VERNE DOFOREST BY W17 ,4

ATTORNEY O DM/ 00 o on a 3 ow 0 mm em v@ I Oct. 15, 1968 w. v. DE FOREST THERMOSTATIC CONTROL DEVICE USING A HALL PLATE 3 Sheets-Sheet 2 Filed June 23, 1967 INVENIOR WESLEY VERNE DeFOREST Oct. 15, 1968 w. v. DE FOREST THERMOSTATIC CONTROL DEVICE USING A HALL PLATE 3 Sheets-Sheet 3 Filed June 23 1967 INVENTOR WESLEY VERNE DaFmEST FIGS ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE A condition responsive control device for controlling temperature or the like has condition sensing means adapted for movement in response to condition variations, a Hall effect plate disposed in a magnetic field, and an operative connection between the Hall effect plate and the sensing means to move the Hall effect plate in the mag netic field whereby its output signal varies in accordance with sensed condition variations.

This application is a continuation-in-part of application Ser. No. 434,789, filed Feb. 24, 1965, now Patent No. 3,344,850.

This invention relates to condition responsive control devices and, more particularly, to a thermostatic control device combined with a Hall effect device.

Conventional thermostatic control devices include temperature sensing means that are movable to make and/or break a switch that controls the circuit for a heating and/or cooling system.

For example, a spiral bimetal element coils and uncoils in response to temperature variations and the free end of the bimetal is adapted to operate the switching contacts in the systems control circuit. Such known prior art devices are confronted with numerous disadvantages, e.g., dust collection on the contacts, additional circuit components for modulation control, and complex circuits for controlling both heating and cooling systems.

It is, therefore, an object of the present invention to construct a thermostatic control device from relatively few parts having a relatively simple principle of operation.

Another object of this invention is to combine a Hall effect device with the sensing means of a condition responsive control device.

The present invention has another object in that the output signal of a Hall effect device is varied in accordance with temperature variations.

It is another object of this invention to mount a Hall effect device on a thermally responsive bimetal.

Another object of the present invention is to move a Hall plate in its magnetic field in accordance with variations in temperature sensed by thermostatic means.

Another object of the present invention is to establish a null position in a magnetic field for a Hall effect device.

The present invention has another object in that a Hall effect plate is disposed in a null magnetic field position between the like facing poles of a pair of spaced magnets.

The present invention has another object in that a heating and/ or cooling system control circuit receives a modulating control signal from a Hall effect device corresponding to the varying demand of the system.

Another object of the present invention is to provide a heating and/or cooling system control device with simple means for selection between a modulating control function and an on-otf control function.

A further object of this invention is to provide a thermostatic control device with automatic switch over from one system to another in a heating and cooling system.

Patented Oct. 15, 1968 In practicing the present invention, a control device having condition sensing means is provided with magnetic means to define a magnetic field, Hall effect means is disposed in the magnetic field and includes input and output means, and an operative connection is made between the Hall effect means and the condition sensing means whereby the Hall effect means is movable in the magnetic field to vary its output signal in accordance with condition variations.

Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a thermostatic control device embodying the present invention;

FIG. 2 is a schematic block diagram of the control circuit for the control device of FIG. 1;

FIG. 3 is a diagram of the electrical circuitry for the components illustrated in FIG. 2;

FIG. 4 is a schematic diagram of a modified form of the control device of FIG. 1;

FIG. 5 is a diagram of the electrical circuitry of a modified amplifier; and

FIG. 6 is a diagram of the electrical circuitry of a modified switching circuit device.

While the present invention may be incorporated in a wide variety of condition responsive devices for controlling conditions such as pressure, fluid flow, liquid level, humidity, etc, it will be described as applied to a thermostatic device for controlling heating and/ or cooling systems. Accordingly, as is illustrated in FIG. 1, such a control device includes a mounting base 10 adapted to be attached to a support such as a wall in the space to be temperature controlled. One end of a temperature setting shaft 12 is rotatably carried by the base 10 and its opposite end has a D-shaped cross section on which a knob or dial pointer 14 is fixed; a scale disc 16 is non-rotatably mounted on the shaft 12 or is otherwise suitably fixed to the base 10 so as to be in cooperative relation to the pointer 14. The scale disc 16 is provided with suitable indicia corresponding to the degrees of temperature; e.g., in a room thermostat, the mid-point of the scale represents 70 F. and the opposite ends thereof, respectively represent 50 F. and F. A thermometer (not shown) may be disposed on the lower side of the disc 16.

A cam plate 18 is fixed to the shaft 12 for rotation therewith and engages a lever plate that defines a cam follower 20 to move the same in response to rotation of the dial pointer 14. One end of the follower 20 is attached to a tension coil spring 22 and its other end is pivotally carried by the base 10 whereby the follower 20 is normally biased in a clockwise direction about its pivoted end, as viewed in FIG. 1, so as to be in continuous engagement with the cam plate 18. Adjacent its pivoted end, the follower 20 carries a stud 24 to which a temperature responsive element is afiixed; the temperature responsive element comprises a spiral bimetal 26 having an inner end secured to the stud 24 as by welding so that its outer or free end moves up and down, as viewed in FIG. 1, in response to temperature variations.

With such an arrangement, the free end of the bimetal 26 is provided with a modulating movementin response to temperature variations; however, a snap mechanism such as an overcenter spring device or a magnet device may be utilized to increase the temperature differential and secure a more positive response for on-otf operation without modulation. Such a snap mechanism in FIG. 1 comprises upper and lower permanent magnet assemblies 28 and 3t respectively, which are adjustably carried by wall portions of the base 16. The magnet assemblies 28 and 39 are disposed on opposite sides of the bimetal 26 adjacent the movable end thereof.

A Hall plate 32 is fixed to the movable end of the bimetal 26 for movement therewith and is disposed between the pole faces of a pair of spaced permanent magnets 34 and 36 that are secured to the base 18 by means of an elongated U-shaped bracket 38. A screw 39 is threaded through one leg of the bracket 38 and engages the upper magnet 34 to define a magnet adjustment means for selectively varying the space between the magnets 34 and 36; such adjustment permits the operating differentials and the heating-cooling operating range to be adjusted. The magnets 34 and 36 are mounted with their north poles toward each other with the Hall plate 32 disposed therebetween; the plane of the Hall plate 32 is approximately parallel to the pole faces of the two magnets. A pair of opposite edges of the Hall plate 32 are electrically connected to input current leads 40 and 42, and another pair of opposite edges are electrically connected to output voltage leads 44 and 46.

The Hall plate 32 is a semiconductor wafer which when placed in a magnetic field generates a voltage at the edges in a direction depending on the field and current directions and in a magnitude proportional to the product of the magnetic field strength and the intensity of the current through the plate 32. The well known Hall effect is briefly characterized in that upon passing a predetermined electrical current lengthwise through a conductive plate, which is influenced by a magnetic field passing through the plate at right angles, there occurs an output signal voltage across the plate transverse to the direction of the impressed current fiow.

In accordance with the present invention the input current is maintained constant and the variation in the output signal voltage is accomplished by moving the Hall plate in a direction parallel with the magnetic field in response to a demand function such as a heating demand or a cooling demand. Thus, the Hall plate movement in the magnetic field is utilized to increase or decrease the output signal from the Hall plate.

The block diagram in FIG. 2 illustrates the control circuit for operation of a heating and cooling system. The power supply station includes a transformer 50 having a primary coil 52 connected to power leads L and L which are lead terminals for input voltage, such as a 120 volt source. The transformer 50 includes two secondard coils, one coil 54 being connected to the Hall plate leads 40 and 42 and the other coil 56 being connected to power supply leads 58 and 60 of an amplifier 62.

A diode D and resistor R are serially connected in lead 42 so that the position of the Hall plate 32 relative to the magnetic field determines the wave form as shown on the output lead 44. The Hall plate leads 44 and 46 are connected to amplifier 62 and the amplifier output leads 68 and 70 are connected to the switching circuit device 76. The switching circuit device includes a pair of heating control output leads 78 and 80 and a pair of cool ing control output leads 82 and 84. The control output leads 80 and 82 are separately connected to the secondary coils 86 and 88, rsepectively, of a transformer 90 that has a primary coil 92 connected to the 120 volt source leads L and L The heating control output lead 78 and the other side of secondary coil 86 are connected to the leads 94 and 95, respectively, of a heating control device 96; the cooling control output lead 84 and the other side of the secondary coil 88 are connected to the leads 97 and 98, respectively, of a cooling control device 99.

It is to be understood tha the specific circuitry for the block components illustrated in FIG. 2 may conform to known components. However, for the sake of completeness in disclosing an operative device, a specific example of the entire circuitry is illustrated in FIG. 3.

The power supply transformer 50 includes a diode D and a resistance R connected in series with the secondary coil 54 and the lead line 42 whereby half wave current is supplied to the Hall plate 32. The transformer 50 also furnishes a regulated power supply to the amplifier 62.

To this extent, a diode D is connected in series with the secondary coil 56 and the lead line 58; a capacitor C is connected in parallel with the diode D and the secondary coil 56, and across the lead lines 58 and 60; a serially connected resistance R and a Zener diode D are connected in parallel with the capacitor C the diode D and the secondary coil 56, and across the lead lines 58 and 60; and a transistor T having its emitter connected to lead line 58, its collector connected to the junction of resistance R at lead line 58 and its base connected to a common tap between resistance R and the diode D The amplifier 62 is powered by the power input leads 58 and 60; a branch circuit from lead 58 is connected to a resistance R which is connected to the signal input lead 64 and a branch circuit from lead 60 is connected to a resistance R, which is connected to a junction between the resistance R;, and the signal input lead 64. The signal input leads 64'and 66 are connected to the bases of transistors T and T respectively, the collectors of which are connected to the signal output leads 68 and 70, respectively. The emitters of transistors T and T are connected together with a resistance R therebetween and a variable resistance VR is connected to the twoemitters and in parallel to the resistance R A second branch circuit from power input lead 58 is connected to a resistance R which is connected to the tap of the variable resistance VR. A second branch circuit from the power input lead 60 is connected to a common junction line extending between the signal output leads 68 and 70 with a branch resistor BR in the lead 68 side and a branch resistor 3R in the lead 70 side of such common junction line.

In the switching circuit device 76, the input lead 72 is connected to a diode D which in turn is connected to the control output lead 84; from the diode D, a first parallel circuit includes a transistor T a diode D a resistance R and a second resistance R that is connected to control output lead 82. A second parallel circuit from diode D includes a silicon controlled rectifier SCR having an anode connected to a common junction in the line to the control output lead 84, a gate or trigger connected to a common junction between resistances R and R and a cathode connected in the line from resistance R to the control output lead 82. The emitter of transistor T is connected in the line from the diode D and the collector is connected to the diode D while the base is connected to a common junction between the input lead 74 and a diode D a resistance R, is connected between such common junction and the line leading to the emitter of transistor The switching circuit device includes circuitry for the control output leads 78 and 80 as that described above for the control output leads 82 and 84. Such circuitry includes the diode D connected to the control output lead 78 and the parallel circuits to the control output lead 80 comprising a transistor T a diode D resistances R and R and resistance R The control output leads 78 and 80 are connected across the secondary coil 86 of the transformer 90 and the lead line 78 includes the heating control device 96. The leads 94 and 95 are connected in series to the relay coil RC of device 96 and a capacitor C is connected in parallel across the coil RC. Similarly, the control output leads 82 and 84 are connected across the secondary coil 88 of the transformer 90 and the lead line 84 includes the cooling control device 99; the leads 97 and 98 are connected in series to the relay coil RC of device 99 and a capacitor C is connected in parallel across the coil RC.

The particular functions of the various components in the electrical circuitry will become apparent from the following description with respect to the sequence of operation of the invention. Assuming that the condition to be controlled is temperature and that the temperature setting dial 14 and shaft 12 are set for a controlling temperature of approximately 75 F., the bimetal 26 positions the Hall plate 32 intermediately between like poles, such as the two north poles, of the two spaced magnets 34 and 36. This intermediate area between the magnets defines a null position where the magnetic flux is equalized so that there is no output signal from the Hall plate 32. On either side of this null position, the Hall plate 32 produces an output voltage of the same form either in phase or 180 out of phase. In the particular arrangement illustrated, a call for heat is sensed by the bimetal 26 which effects an upward movement of the Hall plate 32 from the null position into the magnetic field of upper magnet 34 whereby an in phase output signal results; similarly, a call for cooling causes a downward movement of the Hall plate 32 from the null position resulting in a 180 out of phase output signal. In each case, the amplitude of the output signal depends upon the amount of deflection from the null position; thus, the amplitude of the output signal increases with greater deflection because the Hall plate 32 is moving into the increasing flux density of the magnetic field.

Assuming now that the bimetal 26 is expanded or uncoiled in response to a temperature drop below the set point of 75 F., the Hall plate 32 is accordingly moved upward toward the upper magnet 34. As is illustrated in FIG. 3, the transformer 50 supplies a half wave current across the input leads and 42 and in responding to this call for heat, the Hall plate 32 produces an in phase signal at the output of the leads 44 and 46. The in phase signal is then transmitted through the signal input leads 64 and 66 to the amplifier 62. This heat demand signal is thus amplilied and transmitted through the input leads 72 and 74 to the switching circuit device 76 which selects the proper pair of control output leads for the amplifier signal in accordance with the current phase of such signal. In this example, the in phase signal appears across the heating control output leads 78 and 80 to activate the circuit for the heating relay coil RC, the operating current for such coil being supplied by the secondary coil 86 of the transformer 90. The relay coil then energizes the heat supply means (not shown) which may be gas burning apparatus or electrical heating apparatus. For example, in gas burning apparatus the relay coil RC energizes an on-off valve or the RC coil may be replaced by an electromechanical valve positioner that in turn controls the flow of gas to a burner whereby the gas flow is controlled in accordance with variation of the amplified signal as produced from the modulating bimetal 26.

With the above arrangement it is possible to eliminate the usual time lag between the modulating call for heat and the operation of the heating appliance to satisfy the heat demand. By obtaining instantaneous response the chances of overshooting have been virtually eliminated so that the control device will cycle thermostatically within its set operating differentials.

While modulation is desirable for some instances, there may be other instances where on-otf control is more suitable for particular installations. In such installations, the permanent magnets 28 and 30 are spaced on opposite sides of the bimetal 26 adjacent its free end. Movement of the bimetal 26 in response to a call for heat provides movement toward the heating demand permanent magnet 28 so that as the bimetal 26 comes under the influence of the magnetic flux from magnet 28, the final movement of the bimetal 26 is effected with a snap action. The Hall plate 32 is similarly moved to an on position in the magnetic field of the heat demand magnet 34 and produces an output signal of constant voltage. This constant voltage signal is transmitted through the amplifier 62 and switching circuit device 76, as explained above, and the heating relay coil RC effects energization of an on-off valve controlling the gas flow to the burner. Satisfaction of the heat demand causes the bimetal 26 to contract or coil and as soon as the bimetal force exceeds the magnetic force from the permanent magnet 28, the Hall plate 32 will return to the null position with a snap action; the absence of an output signal from the Hall plate 32 effects deenergization of the heating relay coil RC and movement of the on-off valve to its off position.

In controlling the cooling cycle of the system, the bimetal 26 contracts or coils in response to a temperature increase above the set point of 75 F. and the Hall plate 32 is accordingly moved downward toward the cooling demand magnet 36. The operation for the cooling cycle is substantially the same as that described above for both modulation and on-off control of the cooling relay coil RC in the cooling control device 99. During the cooling cycle the output voltage from the Hall plate 32 is 180 out of phase but has the same Wave form as the heating cycle signal; the wave forms are illustrated in FIG. 2, above and below the appropriate leads to represent the in phase and out of phase signals.

It is common practice to install heating and cooling systems in modern homes and building structures, and for the sake of economy and emciency certain components of the two systems are arranged for common usage. However, in such installations, it has been necessary to provide manual switch over or complex arrangements for semi-automatic switch over between the heating system control and the cooling system control. In accordance with the present invention, a unitary thermostatic control provides fully automatic switch over between the heating and cooling systems.

A modification of the magnetic means for the Hall plate 32 is illustrated in FIG. 4 wherein like reference numerals are used for parts identical to those described in connection with FIGS. l-3, reference numerals with added are used for similar parts that are modified, and new reference numerals are used for new parts. For example, the transformer secondary coil 54 has one lead connected to the Hall plate input lead 40 and its other lead connected through D and R to a conductor 133, which is serially connected to the coil winding of an upper electromagnet 134. A conductor 135 provides a series connection between the coil winding of the upper electromagnet 134 and the coil winding of a lower electromagnet 136 which in turn is connected to a conductor 137 having a common junction tap 139 that is connected to the Hall plate input lead 42. A variable resistance 141 is connected between the conductor 133 and the common junction tap 139.

The sequence of operation of the arrangement shown in FIG. 4 is substantially the same as that described above in connection with FIGS. 1-3 so that only those areas where the sequence of operation is different will be described. Accordingly, the electromagnets 134 and 136 are disposed with like poles facing each other and the winding coils thereof are connected in series with the current input leads 40 and 42 of the Hall plate 32. It is now apparent that the two electromagnets establish the magnetic field means into which the Hall plate 32 is moved from a null position by the bimetal 26. The variable resistance 141 is connected across the two windings of the electromagnets to permit adjustable variation between the magnetic field and the input current to the Hall plate 32. Thus, the variable resistance 141 defines a means for selectively controlling the sensitivity and the operating differentials of the ther mostatic control device. Other arrangements of variable resistor means will permit the heating and cooling operating differentials to be controlled separately, if it is so desired for a particular installation.

The modified amplifier 62 in FIG. 5 operates substantially the same as described above in connection with FIG. 3, so the same reference numerals have been used for identical parts and new reference numerals for different components and only the different components will be described. For instance, a pair of magnetic reed type switches 100 and 101 have coiled windings 162 and 103, respectively, with the leads 1114 and 106 for winding 102 being connected to leads 94 and 95, respectively, of FIG. 3 and with the leads and 107 for winding 103 being connected to leads 97 and 98, respectively, of FIG. 3. Switch 100 has a contact terminal 108 connected to the conductor extending between the emitter of transistor T and one end of the variable resistance VR; similarly, switch 102 has a contact terminal 109 connected to the conductor extending between the emitter of transistor T and the other end of the variable resistance VR. The switches 100 and 101 also have contact terminals 110 and 111, respectively, which are connected together to a common junction 112 in the conductor extending from the resistance R to the tap of the variable resistance VR.

With the arangement of FIG. 5, the magnetic reed switch circuits receive a feedback signal from their corresponding relay coils RC when the firing point is reached on their respective silicon controlled rectifiers SCR and SCR For example, firing of the silicon controlled rectifier SCR energizes the relay coil RC of a heating control device 96 and from leads 94 and 95 transmit a feedback signal to the winding 102; thus switch 100 closes providing an instantaneous increase in gate current which carries the load current past the firing point so as to prevent chattering of the relay. It is thus apparent that the circuitry of FIG. 5 eliminates the need for the snap mechanisms in the thermostat.

The arrangement of FIG. 6 is similar to FIG. 5 in operation but provides a modified switching circuit device 76 for inclusion with the circuitry of FIG. 3. In this instance, a pair of magnetic reed type switches 200 and 201 have coiled windings 202 and 203, respectively, with the leads 204 and 206 for the winding 202 being connected to the relay coil leads 94 and 95, respectively, and with the leads 205 and 207 for the winding 203 being connected to the relay coil lead-s 97 and 98, respectively. Switch 200 has a contact terminal 208 connected to the conductor extending between diode D and resistance R10; Similarly, switch 201 has a contact terminal 209 connected to the conductor extending between diode D and resistance R A second contact terminal 210 for switch 200 is connected to a fixed resistance R which in turn is serially connected to one end of a variable resistance VR the other end of which is connected to the gate or trigger electrode of the silicon controlled rectifier SCR A second contact terminal 211 for switch 201 is connected to a fixed resistance R which in turn is serially connected to one end of a variable resistance VR the other end of which is connected to the gate or trigger electrode of the silicon controlled rectifier SCR With the arrangement of FIG. 6, the magnetic reed switch circuits receive a feedback signal from their corresponding relay coils RC upon firing their respective silicon controlled rectifiers SCR and SCR The two magnetic reed switches operate as described above in connection with FIG. 5, i.e., a feedback signal closes switch 200 (or 201) providing an instantaneous increase in the gate current of the silicon controlled rectifier SCR (or SCR The FIG. 6 circuitry thus defines an alternate arrangement for eliminating the need of the snap mechanisms in the thermostat.

Inasmuch as the present invention is subject to many modifications, variations and changes in detail, it is intended that all matter contained in the foregoing description or shown on the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a control device, the combination comprising condition sensing means including a bimetal element adapted for movement in response to condition variations,

Hall effect apparatus including magnetic field means and Hall plate means,

said Hall plate means being disposed in said magnetic field means and including electrical input and output means, and

means attaching said Hall plate means to said bimetal element,

whereby said Hall plate means is movable in said magnetic field means to vary its output signal in accordance with condition variations.

2. In a control device, the combination comprising Hall effect apparatus including magnetic field means and Hall plate means,

input current means for said Hall plate means,

output signal means for said Hall plate means,

condition responsive means attached to said Hall plate means for moving the same relative to said magnetic field means whereby said Hall plate means is moved through areas of varying flux density of said magnetic field means,

said output signal means presenting an output signal varying between zero and maximum magnitudes in accordance with said condition responsive means,

snap acting vmeans actuating said condition responsive means to cause said Hall plate means to move with a snap movement through the areas of varying flux density whereby the output signal from said output signal means reflects the zero and maximum condi tion variations sensed by said condition responsive means, and

control means connected to said output signal means for operation thereby.

3. In a control device, the combination comprising a pair of spaced magnets defining magnetic field means,

said pair of spaced magnets arranged with like poles facing each other to define a null position therebetween,

a Hall plate intermediately positioned between said spaced magnets so as to be disposed for movement into said magnetic field means through 'said null position,

input current means for said Hall plate,

output voltage means for said Hall plate,

condition responsive means attached to said Hall plate for moving the same into said magnetic field means whereby a voltage signal from said output voltage means varies in magnitude in accordance with movement of said condition responsive means, and

means to adjust said magnets relative to each other whereby said magnetic field means may be adjusted.

4. The combination as recited in claim 3 wherein said pair of spaced magnets comprises permanent magnets.

5. The combination as recited in claim 3 wherein said pair of spaced magnets comprises electromagnets.

6. In a thermostatic control system, the combination comprising Hall effect apparatus including magnetic field means and Hall plate means,

input current means for supplying current at a constant magnitude to said Hall plate means,

output signal means for said Hall plate means,

said Hall plate means being disposed for movement relative to said magnetic field means whereby said output signal means presents a signal of varying magnitude in accordance with the moving position of said Hall plate means in said magnetic field means,

control means including electric circuit means receiving the signal from said output signal means for operation thereby, and

thermally responsive bimetal means attached to said Hall plate means for moving the same in said magnetic field means whereby the magnitude of the signal from said output signal means varies in accordance with temperature variations sensed by said thermally responsive means.

7. The combination as recited in claim 6 wherein said magnetic field means comprises permanent magnet means.

8. The combination as recited in claim 6 wherein said magnetic field means comprises electromagnetic means.

9. In a control device, the combination comprising means for establishing a magnetic field,

Hall plate means disposed so as to be movable in said magnetic field, 1

electrical input means connected with said Hall plate means,

electrical output means connected with said Hall plate means,

temperature sensing means movable in response to temperature variations, and

means attaching said temperature sensing means to said Hall plate means so that said Hall plate means moves in a direction parallel with said magnetic field in response to temperature variations sensed by said temperature sensing means whereby said electrical output means provides an electrical signal corretemperature sensing means.

References Cited UNITED STATES PATENTS Zimmerli 32366 Zoss et a1 73-398 X Schmahl et a1 73-141 Kuhrt et a1. 330-6 X Metzger et a1 73398 X Kimisuke Shirae et a1. 330-6 Markham 236--78 X ROBERT A. OLEARY, Primary Examiner. sponding to the temperature variations sensed by said 5 WAYNER, Assistant Examiner- 

